#include  <sys/time.h>

/* FROM: http://www.gnu.org/s/libc/manual/html_node/Elapsed-Time.html */
     /* Subtract the `struct timeval' values X and Y,
      *         storing the result in RESULT.
      *                 Return 1 if the difference is negative, otherwise 0.  */

int timeval_subtract(struct timeval *result, struct timeval *x,
		     struct timeval *y)
{
    /* Perform the carry for the later subtraction by updating y. */
    if (x->tv_usec < y->tv_usec)
      {
	  int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
	  y->tv_usec -= 1000000 * nsec;
	  y->tv_sec += nsec;
      }
    if (x->tv_usec - y->tv_usec > 1000000)
      {
	  int nsec = (x->tv_usec - y->tv_usec) / 1000000;
	  y->tv_usec += 1000000 * nsec;
	  y->tv_sec -= nsec;
      }

    /* Compute the time remaining to wait.
     *           tv_usec is certainly positive. */
    result->tv_sec = x->tv_sec - y->tv_sec;
    result->tv_usec = x->tv_usec - y->tv_usec;

    /* Return 1 if result is negative. */
    return x->tv_sec < y->tv_sec;
}
